1. Field of the Invention
This invention relates to products used in MRI imaging, specifically providing systems to provide high speed digital video images to the MRI system patient, collect speech data from the MRI system patient and to track and to minimize patient movement within the MRI system. These systems enhance patient cooperation to improve the quality of scanner data collection. The innovations of the present invention will enhance diagnostic effectiveness of MRI imaging, patient comfort, patient safety, and will lower MRI imaging costs.
2. Background Information
Magnetic Resonance Imaging (MRI) allows research and diagnostic imaging of humans and animals. An MRI provides two and three dimensional imaging of internal tissue, and can provide imaging of functioning processes of tissue called Functional MRI or fMRI. MRI involves using a combination of high strength magnetic fields and brief radio frequency pulses to image tissue, typically by imaging the dipole movement/spin of hydrogen protons.
MRI is typically performed in a large magnet in which the patient is confined within a narrow bore. The imaging process typically involves the patient being subjected to loud sounds and vibrations in a very confined space. For clear imaging it is typically required that the patient remain very still, not moving more than a few millimeters over a period of minutes or even hours. Some MRI patients perceive this as a high anxiety inducing environment. It is difficult for patients to remain still, be entertained, be pacified, and communicate in this environment.
There is a great need in the MRI field for systems that can assist the patients in being motionless, can assist the patients in communicating with the technologist, can assist in calming the patients, can assist in entertaining and providing other feedback and desired stimulus to the patients.
These systems or innovations can substantially improve the nature of human MRI imaging and can substantially improve diagnostic effectiveness of such imaging. As noted above, in order to obtain an acceptable or good scan the patient must not move for extended periods of time. It has been estimated that this is a serious problem for over 20% of the MRI patients. Furthermore, with children as MRI patients the yield of effective scans can be below 20%, when using standard MRI methods. Implementing improved systems for providing instructions, feedback, and entertainment, tracking movement, and hearing the patient are believed to increase the yield of acceptable scans to over 90%, making diagnosis and medical treatment more effective. These types of MRI imaging support systems or tools can also provide added safety benefits to the MRI system. An effective MRI patient microphone system would allow the operator to hear comments by the patient during scanning even if they are spoken in a low or modest volume (in contrast to current microphone systems that would generally require a patient to yell to be heard making them in-effective). Another safety benefit of these proposed systems is that the tracking of movement by the patient in real time can alert the operator to signs of patient distress that can be checked out in a timely fashion prior to the patient's condition deteriorating further. This data can also be used by the technician/technologist to assess whether patient movements have been so significant so as to warrant the halt and restart of the scanning session.
The MRI environment requires unique approaches to solving problems due to the high magnetic and radio frequency characteristics of MRI imaging. There are three design challenges that must be overcome in implementing any MRI system. First the MRI involves a very intense magnetic field and intense RF emissions that disrupt common electronics (e.g., transformers and coils). Second MRI requires the devices to show very low ferromagnetic properties (so they are not attracted into the magnetic field or disrupt the homogeneity of that field). Third MRI requires devices to show very low EMF emissions which increase the RF noise of MRI imaging and reduces the quality of the imaging. Specialized devices must be built to operate in this environment.
The present invention integrates three devices or systems in an MRI environment for solving critical needs for MRI patient communication/comfort, control, and safety. The first system is an MRI Digital Video Projection System, the second system is an MRI Motion Tracker and Patient Augmented Feedback System and the third system is an MRI Forward Predictive Noise Canceling Microphone System. The details of these systems and the integration of these systems into an MRI environment are discussed in detail below. The advantages of these individual systems will be clarified by an examination of the background for each system.
MRI Digital Video Projection System. In an MRI environment there are a number of reasons to provide the MRI patient with a video image. There have been a variety of video projection systems for MRI environments to accomplish this. There are four video projection methods currently in use, namely: a) filtered video, b) shielded video, c) fiber optic image projection, and d) projected video. In filtered video, as discussed in U.S. Pat. Nos. 5,076,275, 5,877,732 and 5,432,544, the video passes through a low pass RF filter to eliminate video signals above about 30 MHz. The MRI signal operates at high frequencies typically greater than 64 MHz. The problem with this approach is current computer video displays have signals of much higher frequencies (e.g., 1.65 Gb/s for DVI) and harmonics that pass through the range of frequencies that an MRI recording is very sensitive to. This makes the filtered solution ineffective for many video displays. Shielded video, as described in U.S. Pat. Nos. 5,861,865 and 5,864,331, can shield high frequency signals that pass into the MRI room. However, shielded wire can not sustain the very high frequencies of current generation digital displays over the distances, typically tens of meters, involved between the video/computer device and the video display device in a conventional MRI environment. Fiber optic image projection systems, as described in U.S. Pat. Nos. 4,901,141 and 5,414,459, send the video image from and LCD type display some distance from the magnet through fiber optic bundles (such as in bore scopes). However these bundles are very costly and suffer from fiber drop out causing lost pixels and poor image quality. Past projections systems for MRI environments, such as described in U.S. Pat. No. 5,076,275, have provided CRT or LCD projections which provide an analogue display system. These have projected the image outside of the MRI bore resulting visual images that include extraneous distracting visual information and often do not show the display image due to having part of it obstructed either by a body part or the magnet bore. The LCD systems typically have a problem with slow pixel rise time (e.g., 30 ms rise time) smearing the video for rapidly changing displays and suffering from analog distortion of the video image.
MRI Motion Tracker and Patient Augmented Feedback. In MRI imaging it is critical to minimize body motion during the period of scanning, typically 20-180 minutes, that occurs in the acquisition of the images. This is particularly true regarding head movement for MRI brain imaging. A body part moving in the scanner will change the position of the body tissue, with the change of tissue position substantially degrading the image quality. The body in the magnetic field distorts the uniformity causing variation of the MRI signal return and reconstruction error. There are methods for post processing motion correction (e.g., use of AIR algorithms) but these provide only a partial correction (e.g., operate when motion is less than 5 mm of movement). Many methods have been employed in an attempt to achieve head stabilization: surgical pillows, head vices, bolting of heads, bite bars and use of parallax displays. All of these approaches are unsatisfactory principally because patients do not respond well (e.g., concern about gagging when using bite bars) or they become painful (e.g., head vice) resulting in more movement from the pain or interfere with the task (e.g., visually watching a parallax of multiple points). Techniques have been adapted to optically track surgical instruments in MRI for surgery planning, such as described in U.S. Pat. No. 5,603,318. However these MRI environment tracking techniques are poorly suited for tracking body parts and provide no feedback to minimize movement. Most patients in an MRI environment wish to be compliant. However it is nearly impossible for the patient to sense small movements (1 mm, 1° rotation) of the body part, particularly if they occur over a period of time (e.g., head nodding 0.1° per minute during the course of an hour). What is needed is effective sensing of the movement and augmented feedback to the patient and technician to enable minimizing movement.
MR Forward Predictive Noise Canceling Microphone. There have been a variety of microphone systems in use in an MRI environment. Some of these include sound cancellation, such as described in U.S. Pat. Nos. 5,313,945 and 5,427,102. These existing systems use a method of concurrent noise cancellation in which one microphone is placed to input the noise and a second to input the patient speech and noise. Cancellation is accomplished by subtracting the alleged “noise only” microphone signal from the alleged “speech and noise” microphone signal thereby yielding a speech only signal. However this approach depends on multiple microphones having equivalent sound sampling of the noise and differential sampling of the speech. This can only be approximated because the microphones differ in their response to auditory input and their placement resulting in differential phase and amplitude recording of both the speech and noise.
An object of the present invention is to provide an MRI having systems that can assist the patients in being motionless, can assist the patients in communicating with the technologist, can assist in calming the patients, can assist in entertaining and providing other feedback and desired stimulus to the patients. An MRI which has such systems or innovations can substantially improve the nature of human MRI imaging and can substantially improve diagnostic effectiveness.